1. Field of the Invention
This invention relates to photodetection of images, and more specifically to optical devices for enhancing the quality of images detected by multiple staring detector arrays.
2. Description of the Related Art
A Staring Array Detector (SAD) is a real-time photodetection device which includes solid state optical sensors for converting optical energy into electrical signals. The SAD has a photodetector with a photosensitive surface made up of an array of semiconductor pixels that sense brightness, darkness, and grey tones. Light from an image focused onto the pixels is continually processed by a Readout Integrated Circuit (ROIC) to produce electrical signals representing the intensity of the light. An image is formed by combining the electrical signal from each pixel. The resolution of the image detected by a SAD depends on the size of each pixel, with smaller pixels providing greater resolution. Pixel sizes achieved to date are as small as approximately 400 square micrometers. The size of the image detected, on the other hand, depends on the size of the array, which in turn depends on the size and number of the pixels in each array.
The SADs that have a large array of pixels, on the order of 1028.times.1028 pixels, have the advantage of providing a large surface for image detection. One such SAD is the Aladan Array, manufactured by Raytheon Systems Co. The problem with a large array of pixels is that it has complex circuitry and is expensive to manufacture. One solution to forming a large but less expensive detection surface, or to forming a larger than conventional array, is to place several SADs in contact next to one another with their edges abutting. The combination of the SADs' individual photodetectors provides a large photodetection surface. The problem with this solution, referred to as the edge-butting SAD, is that the ROIC of each SAD forms a boundary surrounding its photodetector. When two SADs are placed next to one another, their ROICs, which have no photosensitive properties, form a non-photosensitive gap between their photodetectors. The gaps cause discontinuities in the image detected, resulting in poor image detection.
One solution which avoids the gaps between the photodetectors of the edge-butting SADs is a SAD that has its ROIC formed only beneath its photodetector surface. One such SAD is the Edge-Butted Array, manufactured by Raytheon Systems Co. The photodetectors of these SADs can contact one another with no ROIC between them, thus eliminating any gaps in the image detected. This approach, however, may be costly and difficult to manufacture.
Another method of image detection using SADs is to form a narrow array of pixels and mechanically move the array across an image to be detected. At each location a portion of the image is detected, and all of the image portions are then combined to form the overall image. One such detector is the BSTS, manufactured by Raytheon Systems Co. The problem with this type of image detector is that it does not provide real-time image detection. At each instant of time, only a portion of an image is detected. If the image changes between two detection locations, portions of two different images are detected, which when combined produce an inaccurate detection of either image.